Environmental Engineering Multiple Choice Questions
31. The amount of residual chlorine left in public water supply for safety against pathogenic bacteria is about
a) 0.01 to 0.05 ppm
b) 0.05 to 0.5 ppm
c) 0.5 to 1.0 ppm
d) 1.0 to 5.0 ppm
Ans:b
32. The dissolved oxygen level in natural unpolluted waters at normal temperature is found to be of the order of
a) 1 mg/litre
b) 10 mg/litre
c) 100 mg/litre
d) 1000 mg/litre
Ans:b
33. The velocity of flow of water in a sedimentation tank is about
a) 5 to 10 cm/sec.
b) 15 to 30 cm/sec.
c) 15 to 30 cm/minute
d) 15 to 30 cm/hour
Ans:c
34. The length of rectangular sedimentation tank should not be more than
a) B
b) 2B
c) 4B
d) 8B
where B is the width of the tank
Ans:c
35. The overflow rate for plain sedimentation tanks is about
a) 500 to 750 litres/hour/ m2
b) 1000 to 1250 litres/hour/ m2
c) 1250 to 1500 litres/hour/m2
d) 1500 to 2000 litres/hour/m2
Ans:a
36. Percentage of bacterial load that can be removed from water by the process of plain sedimentation is about
a) 10 to 25
b) 50
c) 75
d) 100
Ans:c
37. The settling velocity of a particle in a sedimentation tank depends on
a) depth of tank
b) surface area of tank
c) both depth and surface area of tank
d) none of the above
Ans:b
38. The settling velocity of a particle in a sedimentation tank increases if
a) particle size is decreased
b) the surface area of tank is increased
c) the depth of tank is decreased
d) none of the above
Ans:d
39. For a given discharge, the efficiency of sedimentation tank can be increased by
a) increasing the depth of tank
b) decreasing the depth of tank
c) increasing the surface area of tank
d) decreasing the surface area of tank
Ans:c
40. The detention period and overflow rate respectively for plain sedimentation as compared to sedimentation with coagulation are generally
a) less and more
b) less and less
c) more and less
d) more and more
Ans:c
31. The amount of residual chlorine left in public water supply for safety against pathogenic bacteria is about
a) 0.01 to 0.05 ppm
b) 0.05 to 0.5 ppm
c) 0.5 to 1.0 ppm
d) 1.0 to 5.0 ppm
Ans:b
32. The dissolved oxygen level in natural unpolluted waters at normal temperature is found to be of the order of
a) 1 mg/litre
b) 10 mg/litre
c) 100 mg/litre
d) 1000 mg/litre
Ans:b
33. The velocity of flow of water in a sedimentation tank is about
a) 5 to 10 cm/sec.
b) 15 to 30 cm/sec.
c) 15 to 30 cm/minute
d) 15 to 30 cm/hour
Ans:c
34. The length of rectangular sedimentation tank should not be more than
a) B
b) 2B
c) 4B
d) 8B
where B is the width of the tank
Ans:c
35. The overflow rate for plain sedimentation tanks is about
a) 500 to 750 litres/hour/ m2
b) 1000 to 1250 litres/hour/ m2
c) 1250 to 1500 litres/hour/m2
d) 1500 to 2000 litres/hour/m2
Ans:a
36. Percentage of bacterial load that can be removed from water by the process of plain sedimentation is about
a) 10 to 25
b) 50
c) 75
d) 100
Ans:c
37. The settling velocity of a particle in a sedimentation tank depends on
a) depth of tank
b) surface area of tank
c) both depth and surface area of tank
d) none of the above
Ans:b
38. The settling velocity of a particle in a sedimentation tank increases if
a) particle size is decreased
b) the surface area of tank is increased
c) the depth of tank is decreased
d) none of the above
Ans:d
39. For a given discharge, the efficiency of sedimentation tank can be increased by
a) increasing the depth of tank
b) decreasing the depth of tank
c) increasing the surface area of tank
d) decreasing the surface area of tank
Ans:c
40. The detention period and overflow rate respectively for plain sedimentation as compared to sedimentation with coagulation are generally
a) less and more
b) less and less
c) more and less
d) more and more
Ans:c
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